All operations will be performed by the same surgeons. Intraoperative hypoxemia will be defined as decrease in arterial oxygen saturation less than 90% will be treated with increasing of FiO2 to 1.0. Addition of low level of 2 cm H2O of CPAP will be considered if the later fails to correct hypoxemia. 1 Intraoperative fluid therapy will include intravenous infusion of 2 ml/kg/hour of Lactated Ringer's solution and blood losses will be compensated with colloids and with red blood cell concentrates if the hemoglobin levels decreases below 8 to 9 g/dL. Mean arterial blood pressure will be maintained greater than 60 mm Hg using bolus doses of ephedrine 5 mg or phenylephrine 100 ug. Urine output will be maintained to be greater than 0.5 ml/kg/hour.